1. Field of the Invention
The present invention relates in general to a structure of MOSFET. In particular, the present invention relates to a strained silicon carbon alloy MOSFET structure and fabrication method thereof.
2. Description of the Related Art
In the present technology for fabricating metal-oxide-semiconductor field-effect transistor (MOSFET), strained silicon is formed on the relaxed SiGe layer to generate tensile strain. It had been confirmed that hole and electron mobility thereof are improved. Intel Corporation has implemented strained silicon technology into 90 nm process technology. The present technology, however, has the drawback of asymmetrical speed increasing between PMOS and NMOS even under the same Ge content. Theoretically, when using carbon doping to increase strain of the strained silicon channel, a highly increased current driving force and device speed of PMOS, and therefore improved symmetry of the CMOS, is anticipated, in addition, since carbon has a higher phonon energy than that of silicon, when adding carbon into a strained Si channel, the carrier saturation speed in the strained silicon carbon alloy channel exceeds that in the strained silicon channel as phonon energy increases. Furthermore, the added carbon can reduce outdiffusion of boron and phosphorous, so that the source/drain junction and channel has an abrupt doping distribution, preventing short-channel effect and minimizing device dimensions.